`.file STRING'
==============

   `.file' (which may also be spelled `.app-file') tells `as' that we
are about to start a new logical file.  STRING is the new file name.
In general, the filename is recognized whether or not it is surrounded
by quotes `"'; but if you wish to specify an empty file name, you must
give the quotes-`""'.  This statement may go away in future: it is only
recognized to be compatible with old `as' programs.  In some
configurations of `as', `.file' has already been removed to avoid
conflicts with other assemblers.  See Machine Dependent.